Field of the Invention
Embodiments of the invention relate to the field of circuit protection devices. More particularly, the present invention relates to a metal oxide varistor for surge protection.
Discussion of Related Art
Over-voltage protection devices are used to protect electronic circuits and components from damage due to over-voltage fault conditions. These over-voltage protection devices may include metal oxide varistors (MOVs) that are connected between the circuits to be protected and a ground line. MOVs have a unique current-voltage characteristic that allows them to be used to protect such circuits against catastrophic voltage surges. However, because varistor devices are so widely deployed to protect many different type of apparatus, there is a continuing need to improve properties of varistors. For example, it may be desirable to improve operational life and/or performance under high energy surge events. One parameter affecting varistor life expectancy is its energy (Joule) rating. As the energy rating increases, the varistor life expectancy typically increases exponentially, the number of transient pulses that it can accommodate increases and the “clamping voltage” provided during each transient decreases. For protection against high energy pulses improvements in varistor performance may also be desirable. For example, if a very large surge such as a lightning strike occurs, the energy dissipated may exceed that which the varistor can accommodate. Follow-through current as a result of a strike may generate excessive current that completely destroys the varistor. Accordingly, it will be appreciated that improvements are desirable in present day circuit protection device employing metal oxide varistors.